Fuel cell cathode utilizing multiple redox couples

ABSTRACT

Fuel cell oxygen electrode and instant startup fuel cells employing such oxygen electrode. The oxygen electrode operates through the mechanism of redox couples which uniquely provide multiple degrees of freedom in selecting the operating voltages available for such fuel cells. Such oxygen electrodes provide the fuel cells in which they are used a “buffer” or “charge” of oxidizer available within the oxygen electrode at all times.

RELATED APPLICATIONS

[0001] The present invention is a continuation-in-part of co-pendingU.S. patent application Ser. No. 09/797,332, which is assigned to thesame assignee as the current application, entitled “Novel Fuel CellCathodes and Their Fuel Cells”, filed Mar. 1, 2001, the disclosure ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The instant invention relates generally to useful cathode activematerials for fuel cells, more specifically to their use as the cathodematerial for Ovonic instant startup alkaline fuel cells. These inventiveoxygen electrodes open up a tremendous number of degrees of freedom infuel cell design by utilizing reduction/oxidation (redox) couples, suchas metal/oxide couples, or simply couples which provide electrochemicaloxidizer, preferably oxygen, to the fuel cell electrolyte forelectrochemical “combustion”. These redox couples, due to theirelectrochemical potential, provide the fuel cells employing them with anincreased operating voltage that is adjustable by varying the redoxcouple used. Additionally the redox couples provide the fuel cell withthe ability to store oxidizer within the electrode which not onlyprovides for instant startup, but also provides the capability toprovide short surge bursts of energy during demand surges and alsoallows for recapture of regenerative energy.

BACKGROUND OF THE INVENTION

[0003] The instant application for the first time provides oxygenelectrodes, and fuel cells using such electrodes, which use oxidecouples to yield a wide selection of operating voltages. Specifically,the instant inventors have determined materials, which used incombination with hydrogen-side electrodes, particularly with thoseconstructed of Ovonic (Trademark of Energy Conversion Devices, Inc.)hydrogen storage material, both of which, in combination, yield highperformance fuel cells having hydrogen storage capacity within thehydrogen electrode and oxygen electrodes which take advantage oflow-cost, in comparison with the traditional platinum electrodes, oxidecouples which allow selection of specific ranges of operating voltage ofthe electrochemical cells with a broad operating temperature range andthe opportunity to provide instant-start by use of the hydrogen storagecapability of the short-range order available in the material of theOvonic hydrogen electrode.

[0004] As the world's human population expands, greater amounts ofenergy are necessary to provide the economic growth all nations desire.The traditional sources of energy are the fossil fuels which, whenconsumed, create significant amounts of carbon dioxide as well as othermore immediately toxic materials including carbon monoxide, sulfuroxides, and nitrogen oxides. Increasing atmospheric concentrations ofcarbon dioxide are warming the earth; creating the ugly specter ofglobal climatic changes. Energy-producing devices which do notcontribute to such difficulties are needed now.

[0005] A fuel cell is an energy-conversion device that directly convertsthe energy of a supplied gas into an electric energy. Highly efficientfuel cells employing hydrogen, particularly with their simple combustionproduct of water, would seem an ideal alternative to current typicalpower generations means. Researchers have been actively studying suchdevices to utilize the fuel cell's potential high energy-generationefficiency.

[0006] The base unit of the fuel cell is a cell having an oxygenelectrode, a hydrogen electrode, and an appropriate electrolyte. Fuelcells have many potential applications such as supplying power fortransportation vehicles, replacing steam turbines, and power supplyapplications of all sorts. Despite their seeming simplicity, manyproblems have prevented the widespread usage of fuel cells.

[0007] Presently most of the fuel cell R & D is focused on P.E.M.(Proton Exchange Membrane) fuel cells. Unfortunately, the P.E.M. fuelcell suffers from relatively low conversion efficiency and has manyother disadvantages. For instance, the membrane and the electrolyte forthe system is acidic. Thus, noble metal catalysts are the only usefulactive materials for the electrodes of the system. Unfortunately, notonly are the noble metals costly, they are also susceptible to poisoningby many gases, specifically carbon monoxide (CO). Also, because of theacidic nature of the P.E.M fuel cell electrolyte, the remainder of thematerials of construction of the fuel cell need to be compatible withsuch an environment, which again adds to the cost thereof. The protonexchange membrane itself is quite expensive, and because of it's lowproton conductivity at temperatures below 80° C., inherently limits thepower performance and operational temperature range of the P.E.M. fuelcell as the PEM is nearly non-functional at low temperatures. Also, themembrane is sensitive to high temperatures, and begins to soften at 120°C. The membrane's conductivity depends on water and dries out at highertemperatures, thus causing cell failure. Therefore, there are manydisadvantages to the P.E.M. fuel cell which make it somewhat undesirablefor commercial/consumer use.

[0008] The conventional alkaline fuel cell has some advantages overP.E.M. fuels cells in that they have higher operating efficiencies, theyuse less costly materials of construction, and they have no need forexpensive membranes. The alkaline fuel cell also has relatively higherionic conductivity in the electrolyte, therefore it has a much higherpower capability. While the conventional alkaline fuel cell is lesssensitive to temperature than the PEM fuel cell, the platinum activematerials of conventional alkaline fuel cell electrodes become veryinefficient at low temperatures. Unfortunately, conventional alkalinefuel cells still suffer from their own disadvantages.

[0009] For example, conventional alkaline fuel cells still use expensivenoble metal catalysts in both electrodes, which, as in the P.E.M. fuelcell, are susceptible to gaseous contaminant poisoning. The conventionalalkaline fuel cell is also susceptible to the formation of carbonatesfrom CO₂ produced by oxidation of the hydrogen electrode carbonsubstrates or introduced via impurities in the fuel and air used at theelectrodes. This carbonate formation clogs the electrolyte/electrodesurface and reduces/eliminates the activity thereof. The inventiondescribed herein eliminates this problem from the hydrogen electrode.

[0010] Fuel cells, like batteries, operate by utilizing electrochemicalreactions. Unlike a battery, in which chemical energy is stored withinthe cell, fuel cells generally are supplied with reactants from outsidethe cell. Barring failure of the electrodes, as long as the fuel,preferably hydrogen, and oxidant, typically air or oxygen, are suppliedand the reaction products are removed, the cell continues to operate.

[0011] Fuel cells offer a number of important advantages over internalcombustion engine or generator systems. These include relatively highefficiency, environmentally clean operation especially when utilizinghydrogen as a fuel, high reliability, few moving parts, and quietoperation. Fuel cells potentially are more efficient than otherconventional power sources based upon the Carnot cycle.

[0012] The major components of a typical fuel cell are the hydrogenelectrode for hydrogen oxidation and the oxygen electrode for oxygenreduction, both being positioned in a cell containing an electrolyte(such as an alkaline electrolytic solution). Typically, the reactants,such as hydrogen and oxygen, are respectively fed through a poroushydrogen electrode and oxygen electrode and brought into surface contactwith the electrolytic solution. The particular materials utilized forthe oxygen electrode and hydrogen electrode are important since theymust act as efficient catalysts for the reactions taking place.

[0013] In an alkaline fuel cell, the reaction at the hydrogen electrodeoccurs between the hydrogen fuel and hydroxyl ions (OH-) present in theelectrolyte, which react to form water and release electrons:

H₂+2OH⁻→2H₂O+2e⁻(E₀=−0.828 v).

[0014] At the oxygen electrode, the oxygen, water, and electrons reactin the presence of the oxygen electrode catalyst to reduce the oxygenand form hydroxyl ions (OH⁻):

O₂+2H₂O+4e⁻→4OH⁻(E₀=−0.401 v).

[0015] The total reaction, therefore, is:

2H₂+O₂→2H₂O (E₀=−1.229 v).

[0016] The flow of electrons is utilized to provide electrical energyfor a load externally connected to the hydrogen electrode and oxygenelectrode.

[0017] It should be noted that the hydrogen electrode catalyst of thealkaline fuel cell is required to do more than catalyze the reaction ofH⁺ ions with OH⁻ ions to produce water. Initially the hydrogen electrodemust catalyze and accelerate the formation of H⁺ ions and release of e⁻from H₂. This occurs via formation of atomic hydrogen from molecularhydrogen. The overall reaction may be simplified and presented (where Mis the catalyst) as:

M+H₂→2M . . . H→M+2H⁺+2e⁻.

[0018] Thus the hydrogen electrode catalyst must not only efficientlycatalyze the electrochemical reaction for formation of water at theelectrolyte interface but must also efficiently dissociate molecularhydrogen into atomic hydrogen. Using conventional anode material, thedissociated hydrogen is transitional and the hydrogen atoms can easilyrecombine to form hydrogen if they are not used very efficiently in theoxidation reaction. With the hydrogen storage hydrogen electrodematerials of the inventive instant startup fuel cells, hydrogen isstored in hydride form as soon as they are created, and then are used asneeded to provide power.

[0019] In addition to being catalytically efficient on both interfaces,the catalytic material must be resistant to corrosion by the alkalineelectrolyte. Without such corrosion resistance, the electrode wouldquickly succumb to the harsh environment and the cell would quickly loseefficiency and die.

[0020] One prior art fuel cell hydrogen electrode catalyst is platinum.Platinum, despite its good catalytic properties, is not very suitablefor wide scale commercial use as a catalyst for fuel cell hydrogenelectrodes, because of its very high cost resulting from the limitedworld supply. Also, noble metal catalysts like platinum, cannotwithstand contamination by impurities normally contained in the hydrogenfuel stream. These impurities can include carbon monoxide which may bepresent in hydrogen fuel or contaminants contained in the electrolytesuch as the impurities normally contained in untreated water includingcalcium, magnesium, iron, and copper.

[0021] The above contaminants can cause what is commonly referred to asa “poisoning” effect. Poisoning occurs where the catalytically activesites of the material become inactivated by poisonous species invariablycontained in the fuel cell. Once the catalytically active sites areinactivated, they are no longer available for acting as catalysts forefficient hydrogen oxidation reaction at the hydrogen electrode. Thecatalytic efficiency of the hydrogen electrode therefore is reducedsince the overall number of available catalytically active sites issignificantly lowered by poisoning. In addition, the decrease incatalytic activity results in increased over-voltage at the hydrogenelectrode and hence the cell is much less efficient adding significantlyto the operating costs. Overvoltage is the difference between the actualworking electrode potential under some conditions and it's equilibriumvalue, the physical meaning of overvoltage is the voltage required toovercome the resistance to the passage of current at the surface of thehydrogen electrode (charge transfer resistance). The overvoltagerepresents an undesirable energy loss which lowers operating efficiencyand adds to the operating costs of the fuel cell.

[0022] In related work, U.S. Pat. No. 4,623,597 (“the '597 patent”) andothers in it's lineage, the disclosure of which is hereby incorporatedby reference, one of the present inventors, Stanford R. Ovshinsky,described disordered multi-component multi-phase hydrogen storagematerials for use as negative electrodes in electrochemical cells forthe first time. In this patent, Ovshinsky describes how disorderedmaterials can be tailor made (i.e., atomically engineered) to greatlyincrease hydrogen storage and reversibility characteristics. Suchdisordered materials are amorphous, microcrystalline, intermediate rangeorder, and/or polycrystalline (lacking long range compositional order)wherein the polycrystalline material includes topological,compositional, translational, and positional modification and disorder.The framework of active materials of these disordered materials consistof a host matrix of one or more elements and modifiers incorporated intothis host matrix. The modifiers enhance the disorder of the resultingmaterials and thus create a greater number and spectrum of catalyticallyactive sites and hydrogen storage sites.

[0023] The disordered electrode materials of the '597 patent were formedfrom lightweight, low cost elements by any number of techniques, whichassured formation of primarily non-equilibrium metastable phasesresulting in the high energy and power densities and low cost. Theresulting low cost, high energy density disordered material allowed thebatteries to be utilized most advantageously as secondary batteries, butalso as primary batteries.

[0024] Tailoring of the local structural and chemical order of thematerials of the '597 patent was of great importance to achieve thedesired characteristics. The improved characteristics of the hydrogenelectrodes of the '597 patent were accomplished by manipulating thelocal chemical order and hence the local structural order by theincorporation of selected modifier elements into a host matrix to createa desired disordered material. Disorder permits degrees of freedom, bothof type and of number, within a material, which are unavailable inconventional materials. These degrees of freedom dramatically change amaterials physical, structural, chemical and electronic environment. Thedisordered material of the '597 patent have desired electronicconfigurations which result in a large number of active sites. Thenature and number of storage sites were designed independently from thecatalytically active sites.

[0025] Multiorbital modifiers, for example transition elements, provideda greatly increased number of storage sites due to various bondingconfigurations available, thus resulting in an increase in energydensity. The technique of modification especially providesnon-equilibrium materials having varying degrees of disorder providedunique bonding configurations, orbital overlap and hence a spectrum ofbonding sites. Due to the different degrees of orbital overlap and thedisordered structure, an insignificant amount of structuralrearrangement occurs during charge/discharge cycles or rest periodsthere between resulting in long cycle and shelf life.

[0026] The improved battery of the '597 patent included electrodematerials having tailor-made local chemical environments which weredesigned to yield high electrochemical charging and dischargingefficiency and high electrical charge output. The manipulation of thelocal chemical environment of the materials was made possible byutilization of a host matrix which could, in accordance with the '597patent, be chemically modified with other elements to create a greatlyincreased density of electro-catalytically active sites and hydrogenstorage sites.

[0027] The disordered materials of the '597 patent were designed to haveunusual electronic configurations, which resulted from the varying3-dimensional interactions of constituent atoms and their variousorbitals. The disorder came from compositional, positional andtranslational relationships of atoms. Selected elements were utilized tofurther modify the disorder by their interaction with these orbitals soas to create the desired local chemical environments.

[0028] The internal topology that was generated by these configurationsalso allowed for selective diffusion of atoms and ions. The inventionthat was described in the '597 patent made these materials ideal for thespecified use since one could independently control the type and numberof catalytically active and storage sites. All of the aforementionedproperties made not only an important quantitative difference, butqualitatively changed the materials so that unique new materials ensued.

[0029] Disorder can be of an atomic nature in the form of compositionalor configurational disorder provided throughout the bulk of the materialor in numerous regions of the material. The disorder also can beintroduced by creating microscopic phases within the material whichmimic the compositional or configurational disorder at the atomic levelby virtue of the relationship of one phase to another. For example,disordered materials can be created by introducing microscopic regionsof a different kind or kinds of crystalline phases, or by introducingregions of an amorphous phase or phases, in addition to regions of acrystalline phase or phases. The interfaces between these various phasescan provide surfaces which are rich in local chemical environments whichprovide numerous desirable sites for electrochemical hydrogen storage.

[0030] These same principles can be applied within a single structuralphase. For example, compositional disorder is introduced into thematerial which can radically alter the material in a planned manner toachieve important improved and unique results, using the Ovshinskyprinciples of disorder on an atomic or microscopic scale.

[0031] Additionally, in copending U.S. application Ser. No. 09/524,116,('116), the disclosure of which is hereby incorporated by reference,Ovshinsky has employed the principles of atomic engineering to tailormaterials which uniquely and dramatically advance the fuel cell art. Theinvention of '116 application has met a need for materials which allowfuel cells to startup instantaneously by providing an internal source offuel, to operate in a wide range of ambient temperatures to which a fuelcell will be exposed to under ordinary consumer use and to allow thefuel cell to be run in reverse as an electrolyzer therebyutilizing/storing recaptured energy. The hydrogen electrodes of the '116fuel cells are formed from relatively inexpensive hydrogen storagematerials which are highly catalytic to the dissociation of molecularhydrogen and the formation of water from hydrogen and hydroxyl ions aswell as being corrosion resistant to the electrolyte, resistant tocontaminant poisoning from the reactant stream and capable of working ina wide temperature range.

[0032] The next step in the evolution of the fuel cell would be to findsuitable materials to replace the expensive platinum oxygen electrodecatalysts of conventional fuel cells. It would also be advantageous toprovide the oxygen electrode with the ability to store chemical energy(possibly in the form of chemically bound oxygen) to assist in theinstant startup of the fuel cell as well as recapture energy Thus thereis a need within the art for such a material. The invention described inthis application is significant in that it provides the next step in thedevelopment of such electrochemical cells. With this invention, theoxygen electrode can be selected from a broad menu of available possibleredox couples and combinations thereof. These redox couples in additionto providing a store of chemical energy, allow the operating voltage ofthe fuel cell to be selected, choosing the appropriate redox couple,alone or in combination.

SUMMARY OF THE INVENTION

[0033] The present invention discloses a fuel cell which has the abilityto start up instantly and can accept recaptured energy such as that ofregenerative braking by operating in reverse as an electrolyzer. Theinstant startup fuel cells have increased efficiency and poweravailability (higher voltage and current) and a dramatic improvement inoperating temperature range (−20 to 150° C.) The fuel cells of theinstant invention also have additional degrees of freedom over the fuelcells of the prior art in that the voltage output of the cell can betailored and they are capable of storing regenerated energy.

[0034] The oxygen electrodes of the instant fuel cells operate throughthe mechanism of redox reactions which uniquely provide multiple degreesof freedom in selecting the operating voltages available for such fuelcells. Such oxygen electrodes provide the fuel cells in which they areused, particularly alkaline fuel cells, with a level of chemical energystorage within the oxygen electrode itself. This means that such fuelcells will have a “buffer” or “charge” available within the oxygenelectrode at pre-startup.

[0035] The fuel cell oxygen electrode comprises an active materialcapable of reversibly storing energy through the mechanism of a redoxcouple. The electrode has a first surface region situated to be exposedto molecular oxygen which includes a catalytically acting componentpromoting the absorption of oxygen through said first surface region andinto said active material to chemically charge said active materialthrough oxygen absorption.

[0036] The fuel cell oxygen electrodes of this invention may utilizeredox couples, particularly metal/oxides couples selected from the groupof metals consisting of copper, silver, zinc, cobalt and cadmium.Another useful redox couple is the nickel hydroxide/nickel oxyhydroxidecouple disclosed herein above. Multiple redox couples may be used incombination resulting in a synergistic effect providing improvedperformance of the oxygen electrode.

[0037] The fuel cell also employs an anode active material which hashydrogen storage capability. The anode active material is a hydrogenstorage alloy which has excellent catalytic activity for the formationof atomic hydrogen from molecular hydrogen, outstanding catalyticactivity toward the formation of water from hydrogen ions and hydroxylions, and has exceptional corrosion resistance toward the alkalineelectrolyte of an alkaline fuel cell. The anode active material is alsolow cost, containing no noble metals. The materials are robust andpoison resistant. The electrodes are easy to produce, by proven low costproduction techniques. The hydrogen electrode eliminates the use ofcarbon therein, thus helping to eliminating the carbonate poisoning ofthe fuel cell.

[0038] The anode active hydrogen storage alloys useful in the instantstartup fuel cells reversibly absorbs and releases hydrogen and has afast hydrogenation reaction rate and a long shelf-life. The hydrogenstorage alloy is preferably selected from Alkaline Earth-Nickel alloys,Rare-Earth/Misch metal alloys, zirconium alloys, titanium alloys andmixtures or alloys thereof. The preferred hydrogen storage alloycontains enriched catalytic nickel regions distributed throughout theoxide surface of the particulate thereof. The catalytic nickel regionsare 50 to 70 Angstroms in diameter and vary in proximity from 2 to 300Angstroms (preferably from 50 to 100 Angstroms). An example of such analloy has the following composition:

(Base Alloy)_(a)Co_(b)Mn_(c)Fe_(d)Sn_(e)

[0039] where the Base Alloy comprises 0.1 to 60 atomic percent Ti, 0.1to 40 atomic percent Zr, 0 to 60 atomic percent V, 0.1 to 57 atomicpercent Ni, and 0 to 56 atomic percent Cr; b is 0 to 7.5 atomic percent;c is 13 to 17 atomic percent; d is 0 to 3.5 atomic percent; e is 0 to1.5 atomic percent; and a+b+c+d+e=100 atomic percent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 is a stylized schematic depiction of a fuel cell oxygenelectrode used in the fuel cells of the instant invention.

[0041]FIG. 2 is a stylized schematic depiction of an inventive fuel cellhydrogen electrode used in the fuel cells of the instant invention.

[0042]FIG. 3 is a stylized schematic depiction of the instant startupalkaline fuel cell with hydrogen storage electrode and oxide coupleelectrode in a preferred embodiment of the instant invention.

[0043]FIG. 4 is a stylized schematic depiction of an energy supplysystem incorporating the instant startup alkaline fuel cell of apreferred embodiment of the instant invention.

DETAILED DESCRIPTION OF THE INVENTION

[0044] This invention relates to catalysts for oxygen electrodes in fuelcells which operate through the mechanism of redox reactions. Suchoxygen electrodes, or oxidizable electrodes, provide the fuel cells inwhich they are used, particularly alkaline fuel cells, with a level ofelectrochemical energy storage within the oxygen electrode itself. Thismeans that such fuel cells will have a “buffer” or “charge” of reactantavailable within the oxygen electrode at pre-startup which, particularlycombined with hydrogen storage anodes described in copending U.S.application Ser. No. 09/524,116 (the disclosure of which is herebyincorporated by reference), yield instant start fuel cells in generaland more specifically to Ovonic instant start alkaline fuel cells. Suchfuel cells have a built in reserve of hydrogen within the hydrogenelectrode and oxygen electrode reactant (possibly oxygen) in the oxygenelectrode for instant startup (discussed herein below), and have theability to accept the energy of regenerative braking by acting as anelectrolyzer (also discussed herein below). The fuel cell has increasedefficiency and increased power capabilities as compared withconventional fuel cells of the prior art, while dramatically increasingthe operating temperature range of the cell (−20 to 150° C.) The fuelcell is easy to assemble and has the advantage of utilizing proven, lowcost production techniques.

[0045] The present invention also relates to fuel cell hydrogenelectrodes and oxygen electrodes, and an energy supply systemincorporating the present fuel cell. The hydrogen electrode includesmaterials which have inherent catalytic activity as well as hydrogenstorage capacity. The oxygen electrodes utilize redox couples, orcombinations of redox couples acting synergistically, providing for thereduction and storage of oxygen within the oxygen electrode. The oxygenelectrode and hydrogen electrode materials do not need any noble metals,and are therefore inherently low cost. The oxygen electrode and hydrogenelectrode materials are robust and long-lived, being resistant topoisoning. The hydrogen electrode does not utilize the carbon substratesof the prior art. While a detailed discussion of the instant electrodesand their utilization in an alkaline fuel cell is described hereinbelow, it should be noted that the concepts of the instant invention canbe applied to other types of fuel cells (e.g. P.E.M. fuel cells).

[0046] In general, for such fuel cell oxygen electrodes, oxygen isgenerally available to the oxygen electrode on a continuously-suppliedbasis on one side thereof where the catalytically active materialconverts the molecular oxygen into atomic oxygen which is reduced byelectrolyte at the electrolyte contacting surface of the oxygenelectrode to form hydroxyl ions. In prior art oxygen electrodes, nostorage of reactant occurs. That is oxygen travels directly through theactive materials and reacts with the electrolyte at the electrolytecontacting side of the oxygen electrode. In the oxygen electrodes of theinstant invention, oxygen is stored in the oxygen electrode within thereversible redox couples, and is then available, at theelectrode/electrolyte interface of the oxygen electrode. Availableelectrons will then be generated through the electrochemical reactionwith the fuel. Thus the fuel cell will provide a constant supply ofelectricity at voltages characteristic of the redox couple, orelectrochemically reversible redox system (e.g. a metal and its oxide).Additionally, this added benefit may be obtained by redox couples otherthan between the simple combination of a metal and its oxidized form. Anexample of this is the redox couple of cobalt hydroxide/cobaltoxyhydroxide. With such a redox couple system, the fuel cell willprovide a potential whose theoretical voltage limit is the sum of thehydrogen electrode and oxygen electrode reactions. Certainly thetheoretical limit of voltage available is modified or limited by otherconsiderations, particularly including internal resistance of theelectrodes and the complete fuel cell system.

[0047] At the oxygen electrode, the oxygen, water, and electrons reactin the presence of the cathode active material to reduce the oxygen andform hydroxyl ions (OH⁻)

O₂+2H₂O+4e⁻→4OH⁻.

[0048] The flow of electrons is utilized to provide electrical energyfor a load externally connected to the hydrogen electrode and oxygenelectrode. That load is available to be filled by any number of needsincluding, but not limited to, powering motive vehicles, lightingdevices, heating or cooling devices, power tools, entertainment devices,and other electricity-consuming devices too numerous to mention.

[0049] Numerous redox couples exist and may be used alone or incombination to form the oxygen electrode of this invention. When used incombination, the redox couples may complement one another to provideimproved kinetics within the oxygen electrode. The improved kineticswithin the oxygen electrode are a result of the multiple redox couplesassisting each other synergistically.

[0050] When such couples are used, cycling transition from the oxidizedform to the reduced form is accomplished repeatedly and continuously.From a practical point of view, the ability to withstand such cycling ispreferred. Following is a list of potential redox couples that may beused alone or in combination in the oxygen electrode in accordance withthe present invention.

[0051] (1) Co⁺²<------>Co⁺³ (Valency level 2 to a valency level 3)Co(OH)₂+OH⁻-->CoOOH+H₂O+e⁻

[0052] (2) Co⁺²<------>Co⁺⁴ (Valency level 2 to a valency level 4)Co(OH)₂+2OH⁻-->Co(OH)₄+2e⁻Co(OH)₄-->CoO₂+2H₂O

[0053] (3) Ni⁺²<------>Ni⁺³ (Valency level 2 to valency level 3)Ni(OH)₂+OH⁻-->NiOOH+H₂O+e⁻

[0054] (4) Ni⁺²<------>Ni⁺⁴ (Valency level 2 to valency level 4)Ni(OH)₂+2OH⁻-->Ni(OH)₄+2e⁻Ni(OH)₄-->NiO₂+2H₂O

[0055] (5) Ag<------>Ag⁺ (Valency level 0 to valency level 1)2Ag+2OH⁻-->Ag₂O+H₂O+e⁻

[0056] (6) Ag<------>Ag⁺² (Valency level 0 to valency level 2)Ag+2OH⁻-->AgO+H₂O+2e⁻

[0057] (7) Cu<------>Cu⁺² (Valency level 0 to valency level 2)Cu+2OH⁻-->CuO+H₂O+2e⁻

[0058] (8) (Ni/Ag)⁺²<------>(Ni/Ag)

[0059] (9) (Ni/Fe)oxide⁺²<------>(Ni/Fe)oxide⁺³

[0060] (10) Mn⁺²<------>Mn⁺³-->Mn⁺⁷

[0061] (11) Sn⁺²<------>Sn⁺⁴

[0062] Groups 8, 9, 10, and 11 are comprised of multiple elements havingmultiple valency states. The multiple valency states create difficultyin predicting which reaction is predominant in each grouping.

[0063] Amphoteric elements like aluminum, boron, and silicon may also beused when incorporated into appropriate chemical compounds to suppresstheir solubility in alkaline solutions contacting the oxygen electrode.Various mixed oxides, sulfides, and halides may also be used where anyof the above mentioned reactions, alone or in combination, have avalency change linked to them.

[0064] In all of the previously described reactions, the overallreaction is still oxygen reduction. In these reactions the pathwaychosen is not a direct electrochemical reduction of O₂, but via a redoxreaction. This gives another degree of freedom to choose the right redoxreaction, matching the kinetics and the operating potential desired.

[0065] The fuel cell oxygen electrodes of the instant invention alsoinclude a catalytic material which promotes the dissociation ofmolecular oxygen into atomic oxygen (which reacts with the redoxcouple). A particularly useful catalyst is carbon. As discussed hereinbelow this carbon should be very porous and may be electricallyconductive.

[0066] The oxygen electrodes may contain an active material componentwhich is catalytic to the dissociation of molecular oxygen into atomicoxygen, catalytic to the formation of hydroxyl ions (OH⁻) from water andoxygen ions, corrosion resistant to the electrolyte, and resistant topoisoning. A material useful as an active material in the oxygenelectrode is on a host matrix including at least one transition metalelement which is structurally modified by the incorporation of at leastone modifier element to enhance its catalytic properties. Such materialsare disclosed in U.S. Pat. No. 4,430,391 ('391) to Ovshinsky, et al.,published Feb. 7, 1984, the disclosure of which is hereby incorporatedby reference. Such a catalytic body is based on a disorderednon-equilibrium material designed to have a high density ofcatalytically active sites, resistance to poisoning and long operatinglife. Modifier elements, such as La, Al, K, Cs, Na, Li, Ga, C, and Ostructurally modify the local chemical environments of the host matrixincluding one or more transition elements such as Mn, Co and Ni to formthe catalytic materials of the oxygen electrode. These low over-voltage,catalytic materials increase operating efficiencies of the fuel cells inwhich they are employed.

[0067] The oxygen electrode may be formed the same as conventionaloxygen electrodes which use platinum catalysts, but the non-noble-metalcatalysts described above are substituted for the platinum. Thenon-noble catalysts are finely divided and disbursed throughout a porouscarbon matte-like material. The material may or may not have aconductive substrate as needed.

[0068] The fuel cell oxygen electrodes of this invention utilizecombinations of redox couples which provide for oxygen reduction andstorage. The oxygen electrodes of the instant invention may also includea catalytic material which promotes and speeds the dissociation ofmolecular oxygen into atomic oxygen (which reacts with the redoxcouple). A particularly useful catalyst is carbon. This carbon should bevery porous and may be electrically conductive.

[0069] The oxygen electrode also needs a barrier means to isolate theelectrolyte, or wet, side of the oxygen electrode from the gaseous, ordry, side of the oxygen electrode. A beneficial means of accomplishingthis is by inclusion of a hydrophobic component comprising a halogenatedorganic compound, particularly polytetrafluoroethylene (PTFE) within theelectrode.

[0070] The oxygen electrodes, may also include a current collector orcurrent collecting system extending within said active material. Thecurrent collector may comprise an electrically conductive mesh, grid,foam or expanded metal. The choice of such collection systems may bemade according to electrode manufacturing or production system needs.

[0071] The oxygen electrode in the preferred embodiment of the presentinvention has a layered structure and is shown in FIG. 1. The layeredstructure promotes oxygen dissociation and absorption within the oxygenelectrode 10. Each oxygen electrode 10 is composed of a thin A layer 11,a B layer 12, and a C 13 layer with a current collector grid 14 embeddedwithin the C layer 13. The C layer 13 is on the electrolyte contactingside 15 of the oxygen electrode 10 and the A layer 11 is on the oxygencontacting side 16 of the oxygen electrode 10. The A layer 11 may becomposed of carbon particles coated with polytetrafluoroethylene (PTFE).The carbon particles may be acetylene black or Vulcan XC-72, which arewell known in the art. The carbon/PTFE mixture may contain approximately30% PTFE with the remainder comprising carbon, thereby making the carbon30% teflonated. The 30% teflonated carbon is mixed with the redox couplecatalyst. The redox couple catalyst comprises approximately 10% of the Alayer while the 30% teflonated carbon comprises the remaining 90% of theA layer. The B layer 12 may be wholly composed of carbon particlescoated with polytetrafluoroethylene. The carbon particles may be carbonblack known as Vulcan XC-72 carbon (Trademark of Cabot Corp.), which iswell known in the art. The B layer 12 may contain approximately 40percent by weight polytetrafluoroethylene with the remainder consistingof carbon particles. The C layer 13 may contain approximately 65 percenta teflonated carbon mixture, 15% graphite, and 20% redox couplecatalyst. The teflonated carbon mixture may comprise Vulcan XC-72,Acetylene Black, Cabot Black Pearl 2000, or other types of carbon wellknown in the art teflonated to 20%. The graphite is preferably TIMREXSFG 44 graphite (Trademark of Timcal Group). Embedded throughout the Clayer is a current collector grid serving both as a substrate and acurrent collector. Examples of current collector grids include, but arenot limited to, mesh, grid, matte, expanded metal, foil, foam and plate.The cobalt oxide may also contain a lithium-aluminum alloy, gallium, orother modifiers for improved performance.

[0072] Reactive elements such as lithium may be added to the redoxcouple in the form of a non-reactive alloy such as a LiAl alloy. Thatis, lithium alone as an individual element is extremely reactive withoxygen and water vapor, therefore it is advisable to incorporate theelement into the redox couple in the form of an alloy with aluminumwhich is not reactive in this way. Other elements which may be alloyedwith the lithium include boron and silicon. Specifically the LiAl alloyis a 50:50 At. % alloy.

[0073] In a fuel cell the oxygen electrode just described is used inconjunction with hydrogen electrodes. While any functional hydrogenelectrode may be used with the inventive oxygen electrode, preferredembodiments of the fuel cells of this invention will include hydrogenelectrodes employing hydrogen storage alloy active materials. It shouldbe noted that the preferred hydrogen electrode catalyst of the alkalinefuel cell is required to do more than catalyze the reaction of H⁺ ionswith OH⁻ ions to produce water. Initially the hydrogen electrode mustcatalyze and accelerate the formation of H⁺ ions. This occurs viaformation of atomic hydrogen from molecular hydrogen. The overallreaction can be seen as (where M is the hydrogen storage anode activealloy material):

M+H₂→M . . . H→MH→M+H⁺+e⁻.

[0074] That is, molecular hydrogen (H₂) is converted to adsorbed atomichydrogen (M . . . H) onto the surface of the hydrogen electrode. Thisadsorbed hydrogen is very quickly converted to a metal hydride (MH) inthe bulk of the hydrogen storage alloy. This hydride material is thenconverted to ionic H⁺ releasing an electron e⁻. The ionic hydrogenreacts with a hydroxyl ion in the electrolyte to produce water and theelectron is released into the external load circuit. Thus the hydrogenelectrode catalyst must not only efficiently catalyze the formation ofwater at the electrolyte interface but must also efficiently dissociatemolecular hydrogen into ionic hydrogen. Using conventional hydrogenelectrode material, the dissociated hydrogen is transitional and thehydrogen atoms can easily recombine to form hydrogen if they are notused very quickly in the oxidation reaction. With hydrogen storageelectrode materials, hydrogen is trapped in hydride form as soon ashydrides are created. The hydrogen, as electrochemically released intothe electrolyte, are then used as needed to provide the fuel cell'selectrical power output.

[0075] In addition to being catalytically efficient on both interfaces,the hydrogen electrode catalytic material must be resistant to corrosionby the alkaline electrolyte. Without such corrosion resistance, theelectrode would quickly succumb to the harsh environment and the cellwould quickly lose efficiency and die.

[0076] One prior art fuel cell hydrogen electrode catalyst is platinum.Platinum, despite its good catalytic properties, is not very suitablefor wide scale commercial use as a catalyst for fuel cell hydrogenelectrodes, because of its very high cost. Also, noble metal catalystslike platinum, also cannot withstand contamination by impuritiesnormally contained in the hydrogen fuel stream. These impurities caninclude carbon monoxide (which may be present in hydrogen fuel) orcontaminants contained in the electrolyte such as the impuritiesnormally contained in untreated water including calcium, magnesium,iron, and copper.

[0077] The above contaminants can cause what is commonly referred to asa “poisoning” effect. Poisoning occurs where the catalytically activesites of the material become inactivated by poisonous species invariablycontained in the fuel cell. Once the catalytically active sites areinactivated, they are no longer available for acting as catalysts forefficient hydrogen oxidation reaction at the hydrogen electrode. Thecatalytic efficiency of the hydrogen electrode therefore is reducedsince the overall number of available catalytically active sites issignificantly lowered by poisoning. In addition, the decrease incatalytic activity results in increased overvoltage at the hydrogenelectrode and hence the cell is much less efficient adding significantlyto the operating costs. Overvoltage is the difference between theelectrode potential and it's equilibrium value, the physical meaning ofover-voltage is the voltage required to overcome the resistance to thepassage of current at the surface of the hydrogen electrode (chargetransfer resistance). The overvoltage represents an undesirable energyloss which adds to the operating costs of the fuel cell.

[0078] The hydrogen electrodes may be generally composed of an anodeactive material having hydrogen storage capacity. The anode activematerial is designed to have a high density of active catalytic sites,resistance to poisoning, and long operating life to provide efficientlow cost fuel cell operation.

[0079] An anode active material of the instant invention may be acomposite of a hydrogen storage material and an additional catalyticmaterial. The preferable anode active material is one which canreversibly absorb and release hydrogen irrespective of the hydrogenstorage capacity and has the properties of a fast hydrogenation reactionrate, a good stability in the electrolyte and a long shelf-life. Itshould be noted that, by hydrogen storage capacity, it is meant that thematerial stores hydrogen in a stable form, in some nonzero amount higherthan trace amounts. Preferred materials will store about 1 weight %hydrogen or more. Preferably, the alloys include, for example,rare-earth/Misch metal alloys, zirconium and/or titanium alloys ormixtures thereof. The anode material may even be layered such that thematerial on the hydrogen contacting surface is formed from a materialwhich has been specifically designed to be highly catalytic to thedissociation of molecular hydrogen into atomic hydrogen, while thematerial on electrolyte contacting surface is designed to be highlycatalytic to the formation of water from hydrogen and hydroxyl ions.

[0080] Certain hydrogen storage materials are exceptionally useful asalkaline fuel cell hydrogen electrode materials. The useful hydrogenstorage alloys have excellent catalytic activity for the formation ofhydrogen ions from molecular hydrogen and also have superior catalyticactivity toward the formation of water from hydrogen ions and hydroxylions. In addition to having exceptional catalytic capabilities, thematerials also have outstanding corrosion resistance toward the alkalineelectrolyte of the fuel cell. In use, the alloy materials act as 1) amolecular hydrogen decomposition catalyst throughout the bulk of thehydrogen electrode; and 2) as an internal hydrogen storage buffer toinsure that a ready supply of hydrogen atoms is always available at theelectrolyte contacting surface.

[0081] Specific alloys useful as the anode material are alloys thatcontain enriched catalytic nickel regions of 50-70 Angstroms in diameterdistributed throughout the oxide interface which vary in proximity from2-300 Angstroms preferably 50-100 Angstroms, from region to region. As aresult of these nickel regions, the materials exhibit significantcatalysis and conductivity. The density of Ni regions in the alloysprovide powder particles having an enriched Ni surface. The mostpreferred alloys having enriched Ni regions are alloys having thefollowing composition:

(Base Alloy)_(a)Co_(b)Mn_(c)Fe_(d)Sn_(e)

[0082] where the Base Alloy comprises 0.1 to 60 atomic percent Ti, 0.1to 40 atomic percent Zr, 0 to 60 atomic percent V, 0.1 to 57 atomicpercent Ni, and 0 to 56 atomic percent Cr; b is 0 to 7.5 atomic percent;c is 13 to 17 atomic percent; d is 0 to 3.5 atomic percent; e is 0 to1.5 atomic percent; and a+b+c+d+e=100 atomic percent. Such materials aredisclosed in U.S. Pat. No. 5,536,591 to Fetcenko et al., published Jul.16, 1996, the disclosure of which is hereby incorporated by reference.

[0083] The hydrogen electrodes in the preferred embodiment of thepresent invention have a layered structure and are exemplified in FIG.2. The layered structure promotes hydrogen dissociation and absorptionwithin the hydrogen electrode 20. Each hydrogen electrode 20 is composedof an active material layer 21, a current collector grid 22, and aporous polytetrafluoroethylene layer 23. The active material layer 21 isdisposed between the current collector grid 22 and thepolytetrafluoroethylene layer 23. The polytetrafluoroethylene layer 23may be approximately 0.0007 inches thick. The current collector grid 22is on the electrolyte contacting side 24 of the hydrogen electrode 20and the polytetrafluoroethylene layer 23 is on the hydrogen contactingside 25 of the hydrogen electrode 20. The active material layer 21 maybe dispersed throughout the current collector grid 22. Examples ofcurrent collector grids include, but are not limited to, mesh, grid,matte, expanded metal, foil, foam and plate. The current collector gridmay be composed of a conductive material such as nickel, a nickel alloy,copper, nickel plated copper or a copper-nickel alloy. Other conductivematerials may be substituted as required by design constraints. Thehydrogen electrode may also include an electrically conductive powderintimately mixed with the hydrogen storage material which aids incurrent collection. The electrically conductive powder may be formedfrom copper, a copper alloy, nickel, a nickel alloy, and carbon to aid.

[0084] The active material layer 21 may be composed of Misch metalnickel alloy, Raney nickel, graphite, and polytetrafluoroethylenepowder. A preferred composition of the active material layer 21 is byweight 35% Mischmetal nickel alloy, 46% Raney nickel, 4% graphite, and15% polytetrafluoroethylene. The most preferred Misch metal nickel alloyhas the following composition by weight percent:

[0085] 50.07% Ni, 10.62% Co, 4.6% Mn, 1.8% Al, 20.92% La, 8.63% Ce,0.87% Pr, and 2.49% Nd. The graphite may be one with isotropic shapehaving high electrical and thermal conductivity. A typical example ofsuch graphite is called TIMREX KS-75 (Trademark of Timcal Group). Raneynickel and polytetrafluoroethylene are well known in the art and do notneed any further discussion.

[0086] It should be noted that the hydrogen electrode and oxygenelectrode active materials of the instant invention are robust and veryresistant to poisoning. This is true because the increased number ofcatalytically active sites of these materials not only increasescatalytic activity, but enables the materials to be more resistant topoisoning, because with materials of the present invention numerouscatalytically active sites can be sacrificed to the effects of poisonousspecies while a large number of non-poisoned sites still remain activeto provide the desired catalysis. Also, some of the poisons areinactivated by being bonded to other sites without effecting the activesites.

[0087]FIG. 3 is a stylized schematic depiction of an alkaline fuel cell30 incorporating the oxygen electrode 10 and the hydrogen electrode 20of the instant invention. The fuel cell 30 consists of three generalsections: 1) a hydrogen electrode section, which includes the hydrogenelectrode 20 and a hydrogen supply compartment 31; 2) the electrolytecompartment 32; and 3) the oxygen electrode section, which includes theoxygen electrode 10 and the oxygen (air) supply compartment 32.

[0088] In the hydrogen electrode section, hydrogen or hydrogencontaining gas mixtures is supplied under pressure to the hydrogensupply compartment 31 through hydrogen inlet 33. Hydrogen is thenabsorbed through the hydrogen contacting surface 25 into the hydrogenelectrode 20. The absorbed hydrogen is catalytically broken down by theanode active material into atomic hydrogen which is stored in thehydrogen storage material as a hydride, and then finally reacts at theelectrolyte contacting surface 24 with hydroxyl ions to form water. Itshould be noted that the heat of hydride formation helps to warm thefuel cell to it's optimal operating temperature. Any unabsorbed hydrogenand other contaminant gases or water vapor in the hydrogen supply arevented through outlet 34. The gases that are vented may be recycled ifenough hydrogen is present to warrant recovery. Otherwise the hydrogenmay be used to provide a source of thermal energy if needed for othercomponents such as a hydride bed hydrogen storage tank.

[0089] The electrolyte compartment 32 holds (in this specific example)an aqueous alkaline electrolyte in intimate contact with the hydrogenelectrode 20 and the oxygen electrode 10. The alkaline solution is wellknown in the art and is typically a potassium hydroxide solution. Theelectrolyte provides hydroxyl ions which react with hydrogen ions atelectrolyte contacting surface 24 of the hydrogen electrode 20 and watermolecules which react with oxygen ions at the electrolyte contactingsurface 15 of the oxygen electrode 10. The electrolyte is circulatedthrough compartment 32 via inlet 35 and outlet 36 (in alternativeembodiments, the electrolyte may be deliberately immobilized as byjelling, etc.) The circulated electrolyte may be externally heated orcooled as necessary, and the concentration of the electrolyte can beadjusted (as via wicking, etc.) as needed to compensate for the waterproduced by the cell and any losses due to evaporation of water throughthe electrodes. Systems for conditioning the fuel cell electrolyte arewell known in the art and need not be further described in detailherein.

[0090] In the oxygen electrode section, oxygen, air, or some otheroxygen containing gaseous mixture is supplied to the oxygen supplycompartment 32 through oxygen inlet 37. Oxygen is then absorbed throughthe oxygen contacting surface 16 into the oxygen electrode 10. Theabsorbed oxygen is catalytically broken down by the cathode activematerial into ionic oxygen, which finally reacts at the electrolytecontacting surface 15 (via the redox couple) with water molecules toform hydroxyl ions. Any unabsorbed oxygen and other gases in the feed(e.g. nitrogen, carbon dioxide, etc.) or water vapor in the oxygensupply are vented through outlet 38.

[0091] Such fuel cells may, as a system, further comprise an electrolyteconditioning means for conditioning the electrolyte. This electrolyteconditioning system will not only adjust the temperature of theelectrolyte (for optimal fuel cell performance) but will also removewater from the electrolyte. The water removal is necessary because wateris produced as a by-product of the fuel cell's electrochemical hydrogenoxidation reaction. This water, if not removed would dilute theelectrolyte, thus impeding the optimal performance of the fuel cell.

[0092] These fuel cells will further include, as a system, a hydrogensupply source including means for continuously supplying fuel,particularly molecular hydrogen, to the hydrogen electrode's firstsurface region; an oxygen supply source which includes means forcontinuously supplying molecular oxygen to the oxygen electrode's firstsurface region; and an electrolyte conditioning system which includesmeans for continuously conditioning the electrolyte, thereby enablingcontinuous operation of the fuel cell as an electrical power source.

[0093] Fuel cells of the instant invention using oxygen electrode withredox couples, particularly in combination with the hydrogen storageanodes of the '116 application provide the ability to recapture reverseelectrical power flow from an external circuit into said fuel cell,electrolytically producing hydrogen and oxygen which are absorbed andstored through the mechanism of the redox couple in the oxygen electrodeand the hydrogen storage material in the hydrogen electrode. When theinstant fuel cell is run in reverse, as an electrolyzer, during anenergy recapture process such as regenerative braking, water iselectrolyzed into hydrogen and oxygen. In this regenerative brakingmode, the electric motors reverse their roles and become generatorsusing up the kinetic energy of the motion. This causes a spike ofcurrent which amounts to about 10% of the normal operating load. Aconventional fuel cell (alkaline or P.E.M.) cannot accept such surges.This feedback of energy would cause rapid hydrogen and oxygen evolutionwhich would cause the catalysts to lose their integrity and adhesionthereby undermining the overall system performance. In the inventivefuel cell, this will not be a problem, because the hydrogen storageanode and the oxide couple oxygen electrode will take the surge currentand become charged with the produced hydrogen or oxygen respectively.

[0094]FIG. 4 is a stylized schematic depiction of an energy supplysystem 40 incorporating the alkaline fuel cell 30 of the instantinvention. The energy supply system also includes a source of hydrogen41. The source may be of any known type, such as a hydride bed storagesystem, a compressed hydrogen storage tank, a liquid hydrogen storagetank, or a hydrocarbon fuel reformer. The preferred source is a metalhydride storage system. The hydrogen from the source 41 is transportedto the fuel cell 30 via input line 50, and excess gases are ventedthrough output line 51. A portion of the gases from output line 51 maybe recycled to input line 50 through recycle line 52. The energy supplysystem also includes a source of oxygen, which is preferably air foreconomic reasons. The air is drawn into line 53 and then can be passedthrough a carbon dioxide scrubber 42. The air is then transported to thefuel cell 30 via input line 54. Excess air and unused gases are ventedthrough output line 55. Since this gas stream contains no harmful gases,it may be vented to the environment directly.

[0095] The energy supply system may also include an electrolyterecirculation system. The electrolyte from the fuel cell 30 is removedthrough output line 56 and sent to an electrolyte conditioner 43. Theelectrolyte conditioner 43 heats or cools the electrolyte as needed andremoves/adds water as necessary. The conditioned electrolyte is thenreturned to the fuel cell 30 via input line 57.

[0096] Finally the energy supply system includes electrical leads 44 and45 which supply electricity from the fuel cell 30 to a load 46. The loadcan be any device requiring power, but particularly contemplated is thepower and drive systems of an automobile.

[0097] The instant fuel cell and energy supply systems incorporating itare particularly useful for applications in which instant start andenergy recapture are requirements thereof, such as for example inpowering a vehicle. For instance, in consumer vehicle use, a fuel cellthat has the built in fuel and oxidizer storage of the instant inventionhas the advantage of being able to start producing energy instantly fromthe reactants stored in its electrodes. Thus, there is no lag time whilewaiting for hydrogen to be supplied from external sources. Additionally,because hydrogen and oxygen can be adsorbed and stored in the respectiveelectrode materials of the fuel cell, energy recapture can be achievedas well. Therefore, activities such as regenerative braking, etc., canbe performed without the need for an battery external to the fuel cellbecause any reactants produced by running the fuel cell in reverse willbe stored in the electrodes of the fuel cell. Therefore, in essence,fuel cells employing the instant active electrode materials are theequivalent of a fuel cell combined with a battery. In such a systememploying the redox couples oxygen is also able to be stored within theelectrode to a significant degree as an oxidized component of thecouple, preferably a metal/metal oxide couple, a hydroxide/oxyhydroxide,or combinations thereof.

[0098] The novel electrochemical cell of the present invention alsoenables the practice of the method of the invention which, in oneembodiment thereof, comprises the indirect and continuous introductionof both the fuel, preferably hydrogen, and the reactant which oxidizesthe fuel, preferably oxygen, for the continuous operation of theelectrochemical cell as a fuel cell. That is, the hydrogen is, duringoperation, continuously introduced through a catalytic region in thenegative electrode and continuously stored as a hydride in a region ofmaterial in the negative electrode which is capable of reversiblystoring and releasing hydrogen. Simultaneously therewith hydrogen iselectrochemically released from the negative electrode, on itselectrolyte side, to participate in the cell reaction process so thatcontinuous supply at the gas side, storage within, and release ofhydrogen at the electrolyte side of, the negative electrode is madepossible.

[0099] At the same time oxygen is continuously introduced at the gasside of the positive electrode through a catalytic region and chemicallystored as a material in the form of the charged state of an oxide couplewhich participates in the cell reaction. Simultaneously with theintroduction and chemical storage of the oxygen as just explained thematerial of the oxide couple which is in the charged state participatesin the cell reaction to generate electrical power. Thus anelectrochemical cell is continuously operated through the supply to thegas side, storage within, and release from the electrolyte side of, theoxidant so that operation as a fuel cell is enabled. The unique methodof the invention of operation of an electrochemical cell as a fuel cellis thus made possible. In the situations in which the fuel cell is run“backwards” or as an electrolyzer to recapture and store energy, such asfor example, during regenerative braking, the operating nature asdescribed earlier would not be considered to be disruptive to“continuous” operation.

[0100] The drawings, discussion, descriptions, and examples of thisspecification are merely illustrative of particular embodiments of theinvention and are not meant as limitations upon its practice.

1. In a fuel cell, an oxygen electrode including a cathode activematerial having oxygen storage capacity comprising: a combination ofredox couples which provide for said oxygen storage capacity.
 2. Theoxygen electrode according to claim 1, wherein said combination of redoxcouples comprise at least two redox couples selected from the groupconsisting of a Co⁺²—Co⁺³ couple, a Co⁺²—Co⁺⁴ couple, a Ni⁺²—Ni⁺³couple, a Ni⁺²—Ni⁺⁴ couple, a Ag—Ag⁺ couple, a Ag—Ag⁺² couple, a Cu—Cu⁺²couple, a (Ni/Ag)⁺²—(Ni/Ag) couple, a (Ni/Fe)oxide⁺²-(Ni/Fe)oxide⁺³couple, a Mn⁺²—Mn⁺³—Mn⁺⁷ couple, and a Sn⁺²—Sn couple.
 3. The fuel celloxygen electrode of claim 1, further including a hydrophobic component.4. The fuel cell oxygen electrode of claim 3, wherein said hydrophobiccomponent comprises polytetrafluoroethylene (PTFE).
 5. The fuel celloxygen electrode of claim 4, wherein said PTFE is at least one of: a)intimately mixed with said cathode active material; b) graded withinsaid cathode active material; or c) a separate layer incorporated withinsaid oxygen electrode.
 6. The fuel cell oxygen electrode of claim 1,further including a current collector extending within said activematerial.
 7. The fuel cell oxygen electrode of claim 6, wherein saidcurrent collector comprises an electrically conductive mesh, grid, foam,expanded metal, or combinations thereof.
 8. The fuel cell oxygenelectrode of claim 1, further including a catalytic carbon component. 9.In a fuel cell, said fuel cell including a cathode active materialhaving oxygen storage capacity comprising: a combination of redoxcouples which provide for said oxygen storage capacity.
 10. The oxygenelectrode according to claim 9, wherein said combination of redoxcouples comprise at least two redox couples selected from the groupconsisting of a Co⁺²—Co⁺³ couple, a Co⁺²—Co⁺⁴ couple, a Ni⁺²—Ni⁺³couple, a Ni⁺²—Ni⁺⁴ couple, a Ag—Ag⁺ couple, a Ag—Ag⁺² couple, a Cu—Cu⁺²couple, a (Ni/Ag)⁺²—(Ni/Ag) couple, a (Ni/Fe)oxide⁺²-(Ni/Fe)oxide⁺³couple, a Mn⁺²—Mn⁺³—Mn⁺⁷ couple, and a Sn⁺²—Sn couple.
 11. The fuel cellof claim 9, wherein said oxygen storage capacity provides said fuel cellwith instant startup capability.
 12. The fuel cell of claim 9, whereinsaid oxygen storage capacity provides said fuel cell with the ability toaccept recaptured energy by running in reverse as an electrolyzer. 13.The fuel cell of claim 9, wherein said oxygen electrode further includesa hydrophobic component which comprises polytetrafluoroethylene.
 14. Thefuel cell of claim 9, wherein said oxygen electrode further includes acurrent collector extending within said active material.
 15. The fuelcell of claim 14, wherein said current collector comprises anelectrically conductive mesh, grid, foam or expanded metal.
 16. The fuelcell of claim 9, wherein said oxygen electrode further includes acatalytic carbon component.
 17. The fuel cell of claim 9, wherein saidfuel cell further includes a hydrogen electrode, said hydrogen electrodeincluding an anode active material having hydrogen storage capacity. 18.The fuel cell of claim 17, wherein said hydrogen storage capacityadditionally provides said fuel cell with instant startup capability.19. The fuel cell of claim 17, wherein said hydrogen storage capacityadditionally provides said fuel cell with the ability to acceptrecaptured energy by running in reverse as an electrolyzer.
 20. The fuelcell of claim 17, wherein said hydrogen storage capacity providesthermal energy to said fuel cell via the heat of formation of thehydride thereof.
 21. The fuel cell of claim 17, wherein said anodeactive material is a hydrogen storage alloy which does not include noblemetal catalysts.
 22. The fuel cell of claim 21, wherein said anodeactive material is resistant to poisoning.
 23. The fuel cell of claim21, wherein said hydrogen storage alloy is selected from the groupconsisting of Alkaline Earth-Nickel alloys, Rare Earth/Misch metalalloys, zirconium alloys, titanium alloys, and mixtures or alloysthereof.
 24. The fuel cell of claim 23, wherein said hydrogen storagealloy has the following composition: (BaseAlloy)_(a)Co_(b)Mn_(c)Fe_(d)Sn_(e) where the Base Alloy comprises 0.1 to60 atomic percent Ti, 0.1 to 5 40 atomic percent Zr, 0 to 60 atomicpercent V, 0.1 to 57 atomic percent Ni, and 0 to 56 atomic percent Cr; bis 0 to 7.5 atomic percent; c is 13 to 17 atomic percent; d is 0 to 3.5atomic percent; e is 0 to 1.5 atomic percent; and a+b+c+d+e=100 atomicpercent.
 25. The fuel cell of claim 17, wherein said hydrogen electrodefurther includes a hydrophobic component.
 26. The fuel cell of claim 25,wherein said hydrophobic component is polytetrafluoroethylene (PTFE).27. The fuel cell of claim 26, wherein said PTFE is intimately mixedwith said hydrogen storage alloy.
 28. The fuel cell of claim 26, whereinsaid PTFE is a layer within said hydrogen electrode.
 29. The fuel cellof claim 17, wherein said hydrogen electrode additionally includes asubstrate component which provides only for electrical conductivity andcomprises an electrically conductive powder intimately mixed with saidhydrogen storage material.
 30. The fuel cell of claim 29, wherein saidelectrically conductive powder comprises at least one material selectedfrom the group consisting of copper, a copper alloy, nickel, a nickelalloy, and carbon.
 31. The fuel cell of claim 17, wherein said hydrogenelectrode additionally includes a substrate component which provides forboth electrical conductivity and mechanical support and comprises anelectrically conductive mesh, grid, foam, matte, foil, foam, plate, orexpanded metal.
 32. The fuel cell of claim 31, wherein said substratecomponent comprises an electrically conductive a mesh, grid, foam, orexpanded metal.
 33. The fuel cell of claim 32, wherein said mesh, grid,foam, or expanded metal is formed from nickel or nickel alloy.
 34. Thefuel cell of claim 32, wherein said mesh, grid, foam, or expanded metalis formed from copper, nickel plated copper or a copper-nickel alloy.